First you must graph the function you want to take the integral of. Then, while you're in the graphing screen, go to the math menu. In there is the integral command, and it'll ask you for the lower bound and upper bound for the integral. Note that both of these must be within the graphing window.

Since you make me actually find my 83 from the giant stack of crap on my desk...

Go to the Y= menu, set a function into Y1. Then, press 2nd / TRACE (CALC) / 7: [itex]\int [/itex]f(x)dx. It will take you to the graphing screen and ask you for the boundaries. Put them in, and it spits out the answer at the bottom of the screen.

Since you make me actually find my 83 from the giant stack of crap on my desk...

Go to the Y= menu, set a function into Y1. Then, press 2nd / TRACE (CALC) / 7: [itex]\int [/itex]f(x)dx. It will take you to the graphing screen and ask you for the boundaries. Put them in, and it spits out the answer at the bottom of the screen.